Method of protecting selected parts of heating units



Dec. 24, 1935.

P. C. KEITH, JR

Filed Dec. 6, 193s ////////H/ f f f 1/ INVENTOR R., J H .J E K C. m C RE P ATTORNEY Patented Dec. 24, 1935 UNITED STATES PATENT OFFICE METHODOF PROTECTING SELECTED PARTS OF HEATING UNITS Percival C. Keith, Jr.,Peapack, N. J., assignor to Gasoline Products Company, Inc., Newark, N.J., a corporation of Delaware This inventiion relates to a method ofprotecting selected parts of heating units from excessive heat and hasreference particularly toa method of protecting certain portions ofheating units which are normallyexposed to radiant heat, in which someof the intense radiant heat is caused to be reflected from the surfaceof the tubes rather than being absorbed thereby.

As an illustration, the invention is of advantage in protecting certainparts of tubular heating coils exposed to excessive radiant heat suchas, for example, in protecting parts of heating coils mounted in theradiant heat sections of furnaces such as are employed in the treatmentof hydrocarbon oils.'

As a further illustration, the invention is of particular merit whenapplied to furnaces for the treatment of hydrocarbon oils in which aplurality of separate streams of oil are heated in independent tubularheating units or coils mounted in a single furnace setting.

In the latter case the separate streams of oil in the independentheating coils ordinarily require different temperature treatment. It hasbeen customary when different temperatures are required to control thefiring of the furnace so as to bring the oil in all of the coils to thedesired temperatures. Generally the temperatures of one or more streamsmay be controlled byV regulating the firing of the furnace In someinstances When one or more of the streams pass through a convectionheating zone and then through radiant heating zones, the temperatures ofthese streams are controlled by regulating the volume of oil passingthrough the various coils as well as regulating the firing of thefurnace in the radiant heating Zones. The quantity of oil being passedthrough the various zones depends on the pressure employed. However,since the treatment to which these oils are subjected ordinarilyrequires that they be maintained Within pre-determined pressure ranges,the regulation of the pressure to control the temperature is limited andit may often happen that a portion or all of the individual coilsbecomes overheated necessitating replacements or repairs.

Also it may be desired to reduce the temperature to which the oil isheated, in one or more of the heating coils, below that to which it wasintended to be heated at the time the heating coils were installed Whilemaintaining original temperature conditions for the oils in theremaining coils.

Furthermore, certain portions of the heating coil or other heating unitmay become overheated during normal operating conditions. My inventionis particularly adapted to protect such overheated parts.

One of the primary objects of the invention is to protect selected partsof a heating unit against excessive heat.

A further object of the invention is to cover ycertain selected parts ofa heating unit with a radiant heat reflecting surface capable of beingreadily applied thereto.

A further and more specific object of the invention is to covercertainselected parts of a tubular heating coil employed for heatinghydrocarbon oils with .a uid of paint-like consistency capable ofreflecting radiant heat.

I shall now describe suitable materials that may be used in accordancewith my invention for protecting certain parts of a heating unit with aradiant heat reflecting surface. The radiant heat reflecting surfacetobe. applied to the part or parts to be protected is preferably made upas a paint-like mass of paint-like consistency that is capable of beingapplied by a paint brush or the like, or if desired, by any suitablespraying or dipping method. Wherever the expression paint-like mass orpaint-like consistency is used in the specication and claims, it is tobe understood that the expression includes any material capable ofreflecting radiant heat and applied, as desired, to provide a closelyadhering surface to the part or parts to be protected. The paintlikemass may be prepared as a freely owing iiuid, the thickness thereofVarying from a freely owing fluid to a mass of paste-like consistencywhich may be applied as a thin film or layer of closely adheringmaterial. Y In accordance with the preferred embodiment of theinvention, the part'to be protected from excessive radiant heat isprovided With a thin coating or covering of white pigment suspended in asuitable vehicle such as, for example, sodium silicate to form apaint-like mass which, after being applied and dried, forms a hard andimpervious coating.

While sodium silicate is mentioned as being particularly suitable as avehicle because of its refractory characteristics and because itproduces a hard and impervious coating, it is to be understood thatother types of vehicles may also be employed. It has been found, forexample, that a White pigment such as finely divided calcium oxide in anoil suspension is entirely suitable for the purpose intended. A

As a pigment it is preferred to use an inorganic oxide or salt ratherthan an organic material because of the latters tendency to decompose athigher temperatures. Among the pigments which may be used to advantage,are white metallic oxides such as calcium or lead oxides and salts suchas barium sulphate or zincl sulphide or a mixture of these latter two,commonly called lithopone.

It is preferred, however, to use a white metallic oxide or salt whichdoes not react with sulphur gases normally present in a furnaceatmosphere so as to form a resulting compound of difierent heatreflecting characteristics. Lead oxide, for example, reacts with sulphurto form a black sulphide and consequently would not ordinarily bedesirable as a pigment for fired tubes when the combustion gases containsubstantial amounts of sulphur.

As an example of a suitable composition to be applied to the selectedpart to be protected I may mix lithopone, which as before statedconsists of a mixture of zinc sulphide and barium sulphate with hydratedsodium silicate, sometimes referred to as water glass, and add to themixture sufficient water to make a paint-like mass capable of beingapplied in any desired manner on the portion of the tubes or other partsdesired to be protected. The sodium silicate, upon drying, forms a hardglass-like surface and causes the pigment to firmly adhere to thesurface of the tube.

As another example, I may suspend a pigment such as barium sulphate,calcium oxide or zinc sulphide in a light oil medium which may besprayed or brushed on the parts to be protected. The oil upon beingsubjected to the temperature of the furnace will decompose leaving the.white pigment on the surface of the parts.

As a further example, a plurality of coats of colloidal lime in aqueoussuspension may be applied to the part or parts to be protected.

While my invention is particularly directed to covering the parts to beprotected with a paintlike mass, other radiant heat reflecting surfacesmay be used. For example, the parts may be provided with an electrolyticdeposit of metal such as chromium or chromium alloys, or a sprayed metalcoating Aof chromium, aluminum or other similar metals or alloys havinga high luster. As a further example, the tubes or heating unit to beprotected may be covered with a white procelain or vitreous glazedenamel.

The accompanying drawing illustrates a conventional box type furnacehaving banks of tubes for heating hydrocarbon oils in which the tubeslocated adjacent the roof directly above the fire chamber and the tubesin the rst two rows in the convection zone may be protected ashereinbefore described. It is undertood, however, that the invention isalso of advantage in other types of furnaces and for protecting tubes orother selected parts located in zones other than that illustrated.

Referring to the drawing the furnace chamber I is divided by a fire wall2 into a combustion chamber 3 and `a convection chamber 4. Thecombustion chamber 3 is red by any suitable means such as a burner 5 andthe products of combustion after passing through the combustion chamberflow over the iire wall 2 and down through the convection zone 4 inwhich they impinge directly upon tubes 6. rIlhe combustion gases arewithdrawn from the convection chamber 4 through the flue 'I which mayycommunicate with a stack (not shown) As illustrated, banks of heatingtubes 8 and 9 which may be suitably interconnected to extend around thefour walls of the combustion chamber are adapted to be heated by radiantheat from the products of combustion produced by the burner 5. Thefurnace may also be provided 5 with banks of heating tubes III adjacentthe roof which may be in communication with the tubes 8 and 9 located inthe combustion zone. If desired, the roof tubes I0 may communicate withtubes I2 mounted in the upper portion of the 10 convection Zone, suchfor example as the two top rows of tubes in the convection zone. While Ihave shown tubes 8 'and 9 within the radiant heating zone to form twocoils, it is to be understood that only a single coil may be used. It 15is also to be understood that the two upper rows of tubes I2 in theconvection heating zone 4 may be dispensed with.

In heating hydrocarbon oils in a furnace of the type described, a streamof oil may be introduced 20 into the lower row of tubes 6 and passedcountercurrent to the combustion gases therein to be preheated. The thuspreheated oil may then be conducted through the tubes 8 and 9 which aresubjected to radiant heat in the combustion 2:5l chamber 3 from whichthe oil passes to the two upper rows of convection tubes I2. The oilleaving the convection tubes I 2 may be conducted to any apparatussuitable for carrying out the desired separation of the constituents ofthe oil. 30 While the heating of one stream of oil has been described,it should be understood that two streams of oil may be heated in asimilar manner, one stream thereof passing through certain of the tubesin each of the heating sections and 35 the other stream through theremaining tubes in these heating sections.

It has been found that the roof tubes I0 directly above the combustionchamber are subjected to intense radiant heat with the result 40 thatthe oil passing through them may be too intensely heated and the tubesmay become damaged. In addition to the roof tubes, experience has alsoshown that the first rows of tubes in the convection zone, such as tubesI2, may also be 45 subjected to severe conditions due to the radiantheat from the roof of the furnace directly above, in addition to theintense convection heat from direct impingement of the combustion gases.In

accordance with my invention, overheating of the 50 oil and possibledamage to the tubes subjected to the intense heat may be avoided. Thesetubes, such as the tubes I0 and I2 may be provided with a protectivecovering I I of a composition such as hereinbefore described which whenapplied forms 55 a protective film or layer of material, capable, whendry, of reflecting intense heat and particularly intense radiant heat.

If desired, the oil may be progressively heated during its passagethrough the tubes 6, 8, 9 and 60 I and maintained at the desiredconversion temperature in the two upper rows of tubes l2, which in thisinstance, may function as a soaking section for the oil. When the twoupper rows of tubes I2 are to be dispensed with, the roof tubes 65 Il]may function as a soaking section for the oil.

In operating the furnace in such a manner as to accomplish the desiredsoaking of the oil in either of the `above described soaking sections,it may only be necessary to impart sufficient heat 70 to the oil passingthrough these tubes to counterreact the heat lost by the heat ofcracking. These tubes being subjected to the intense heat in the furnacemay be provided with the protective covering II of the composition andin the manner 75 hereinbefore described. By providing a reecting heatsurface for these tubes, it Will be clear that some of the heat thatwould normally be imparted to the oil passing therethrough is reflectedtherefrom thereby permitting only the neecssary heat to reach the oil asis required to maintain it at the desired conversion tempera.- ture, orif desired, to slightly raise it in temperature.

While I have described applying my invention to certain parts of theheat absorbing surfaces Within the furnace, it is to be clearlyunderstood that it may be applied to other parts, the applicationthereof depending upon the parts that are subjected to the intense heatand should be protected.

Animportant advantage of the invention is that the coating may beapplied in situ and can be applied to any parts of the tubes subject tooverheating.

While the invention has many specic advantages in connection withtubular heating coils, particularly coils used for the treatment ofhydrocarbon oils, it will -be apparent that the invention is alsoapplicable to other types of heating units in which it is desired toprotect a portion of the unit from excessive heat.

Having thus described some of the preferred embodiments of theinvention, it is understood 5 that other modifications and variationscome Within the scope and spirit thereof, and that the invention is notto be limited except as necessary to distinguish from prior art.

I claim: 10

'I'he method of increasing the heat reflecting capacity of selectedparts of a tubular heating coil exposed to radiant heat that comprisespainting the selected parts with a paint comprising a White pigmentcapable of being subjected to nor- 15 mal furnace conditions Withoutmaterial discoloration and a vaporizable vehicle and applying heat tothe heating coil to eiect vaporization of the vehicle and x the pigmenton the painted surfaces as a relatively thin closely adherent 20 lightcolored layer of material capable of reflecting radiant heat. 4

PERCIVAL C. KEITH, JR.

